Alves, AR, Marta, C, Neiva, HP, Nunes, C, Izquierdo, M, and Marques, MC. Modeling fitness variable responses to training in prepubescent children. J Strength Cond Res 34(8): 2352–2359, 2020—The aim of this study was to determine strength and oxygen uptake (V̇o2max) performances according to different training program intervention design with 8-week duration in prepubescent children through a multiple linear regression models. Two hundred forty-five healthy prepubescent children (aged 10.9 ± 0.5 years) were randomly assigned to a specific training program (strength training only—S; aerobic training only—A; intrasession aerobic and strength training—AS; intrasession strength and aerobic training—SA; or concurrent training performed in different sessions—CT) or a control group (no training regimen—C). It was possible to develop indirect predictive models for each training method, by including each variable pretraining, body fat percentage and body mass index. The models provided explained 82% of variance in the V̇o2max, 98% in the 1 kg ball-throw, 96% in the 3 kg ball-throw, 92% in the countermovement jump, 93% in the standing long jump and 98% in the 20 m sprint performances. This novel approach to training evaluation and control aims to provide a tool to allow professionals to calculate changes with a high confidence level (CI 95%), to control gains and to choose the best training methodology to apply according to the defined purposes. The results of this study could be a great support to teachers, coaches, and professionals providing important tools to improve the efficacy and individualization of training.